Good guardian, bad parent: tradeoffs between territory defense and parental care in Darwin’s finches

Although defending a territory may benefit individuals by allowing them to retain important resources, the time and energy costs associated with territory defense may lead territory owners to neglect other reproductively important behaviors. In this study, we assessed the potential trade-off between territory defense and parental care in four Darwin’s finch species on Floreana Island, Galápagos. Using song playback, we simulated territory intrusions to measure male aggressiveness across multiple stages of the breeding cycle (unpaired, paired, incubating, and chick feeding). To quantify parental care at each nest, we conducted one-hour observations to record the frequency of male food deliveries and the duration of female incubation and brooding. Male aggressiveness towards a perceived intruder did not change across the breeding cycle and was highly repeatable (adjusted R = 0.597), although their responses became less vocal across the breeding cycle. A male’s aggressiveness did not predict his frequency of food deliveries during incubation or chick feeding, although females paired with more aggressive males spent significantly less time incubating. This finding provides weak evidence for a trade-off between territory defense and parental care, although the behavioral mechanisms mediating this relationship remain uncertain. Finally, males with aggressive and non-aggressive behavioral phenotypes did not differ in their hatching success, although additional work is needed to assess other measures of individual fitness.